The function of a hinge is typically to support a door, gate, panel or similar device for pivoting movement between a closed position inside a framed opening and an open position outside the opening. The hinge is typically designed so that the panel is movable only about the pivot axis of the hinge. Therefore, when the panel is moved to the closed position, it is usually aligned within the framed opening.
Sometimes, it is desirable to permit the panel to move axially along the hinge axis as well as to pivot about the hinge axis. This can create problems when the panel is moved to the closed position and the panel is not aligned with the framed opening. For example, such misalignment can prevent the panel from closing properly. In addition, any overlap between the panel and the frame can result in damage to these components when they contact each other during closing.
A situation where it is desirable for the panel to be movable axially along the hinge line involves the cowl panels on an aircraft jet engine. Referring to FIG. 1 of the drawings, there is shown a conventional aircraft jet engine indicated at 20 having inlet cowl 22 at the forward end of the engine, a pair of opposing curved, C-shaped thrust reverser panels 24 (only one of which is shown) at the rear end, and a pair of fan cowl panels 26 (only one of which is shown) positioned intermediate between the inlet cowl 22 and the thrust reverser panels 24.
In order to provide access for mechanics to an engine 28 located behind the panels, both fan cowl panels 26 are movable between a closed position shown in FIG. 1 and an open position shown in FIG. 2 where only the port fan cowl panel is shown open. As shown in FIG. 3, the fan cowl panel 26 is connected to a forward extending beam 30 of a strut 31 by three (forward, middle and aft) upper hinges 32 which allow the bottom of the panel 26 to be moved upward and outward from the engine 28 as shown in FIG. 2.
In conventional hinge design for engine cowl panels, the fan cowl panel 26 is free to move in a fore and aft direction along an axial hinge line designated by a line numbered 33 in FIG. 2. More particularly, each hinge 30 has a longer axial dimension than the width of the fitting (not shown) which attaches the panel 26 to the hinge 30. This allows the panel 26 to have a limited amount of movement in the fore and aft direction (relative to the engine) along the hinge axis 33.
The purpose of designing the hinge 32 to allow such axial freedom of movement is to prevent reacting certain flight loads to the hinge. More specifically, during flight when the fan cowl 26 is in the closed position, it is joined with the inlet cowl by a conventional blade and groove arrangement indicated at 34 in FIG. 4. That is, a forward edge portion 36 of the fan cowl 26 includes an annular blade (known as a "V-blade") 38 which projects inward from the inner surface of the fan cowl 26 and which extends vertically between the top and bottom of the fan cowl. When the fan cowl 26 is in the closed position, the blade 38 fits inside an annular groove 40 (known as a "V-groove") which extends vertically between the top and bottom of the inlet cowl 22 at a rear edge portion 42 of the inlet cowl.
Because there can be significant relative motion between the engine 28 and the inlet cowl 22 (with the fan cowl 26 firmly attached thereto), the fan cowl hinges 32 take both vertical and side loads, but do not take loads in the axial direction. That is, certain loads are transmitted axially to the fan cowl 26 from the inlet cowl 22. To avoid reacting these loads at the fan cowl hinges 26 and thereby avoiding possible damage to these hinges, the fan cowl hinges are designed as discussed above to permit movement of the fan cowl panels 26 relative to the strut 31 in an axial direction along the fan cowl hinges 32.
Although the aforementioned conventional design avoids unwanted loading of the fan cowl hinges 32 in the axial direction, it results in problems during the closing of the fan cowls 26 after completing ground maintenance on the engine. During the maintenance activity, it is possible for the fan cowl panel 26 to be pushed up against the forward or rear portions of the hinge fitting thereby causing misalignment.
More specifically, during closure it is difficult to properly align the fan cowl panels 26 between the inlet cowl 22 and the thrust reverser panels 24 so that the V-blade 38 is aligned with the V-groove 40 (FIG. 4). Moreover, these panels are quite large, can be difficult to maneuver, and provide a broad area which is subject to being blown and buffeted by wind. Furthermore, it is difficult for the maintenance personnel who are positioned below the engine, to determine whether the fan cowl panel 26 is properly aligned so that the V-groove blade 38 is aligned with the V-groove 40 at the top part of the engine during the initial portion of the closing sequence.
A typical problem during the initial part of the closing sequence occurs at the upper part of the engine when the forward edge 36 (FIG. 2) of the fan cowl panel 26 overlaps a rearward edge 42 of the inlet cowl so that the V-groove blade 38 is misaligned with the V-groove 40. When the mechanic closes the fan cowl panel, the V-blade 38 either misses the V-groove 40 entirely (fan cowl 26 fully aft) or the segment of the V-blade 38 nearest the hinge 30 contacts the inlet cowl structure forward of the V-groove 40. This can cause significant damage to the fan cowl and surrounding structure. In most of these instances, the mechanic is unaware that damage is occurring because the area of damage is out of view (on top of the engine) where there are large leverage forces at the misaligned contact points.